Revenues - Contract Liabilities (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Contract with Customer, Liability [Abstract]
Opening balance	$ 146	$ 2
Revenue recognized that was included in the contract liability balance at the beginning of the period	(37)	(2)
Increase due to consideration received, net of revenue recognized during the period	3	73
Closing balance	$ 112	$ 73